This application relates to light transmitting panels useful in the architectural and design fields.
Many applications in the architectural and other design fields benefit from visually uniform, rigid, lightweight, light-transmitting structural panels that can be utilized not only to divide space or provide support, but also to transmit or manipulate light and provide privacy. For example, light transmitting panels may be incorporated into furniture, exhibits, residential or office walls, fixed or movable partitions, ceiling panels, work surfaces, shelving, sign panels, light diffusers, flooring, roofing and the like.
There are a number of qualities which are desirable in such light transmitting panels. They are preferably visually uniform to provide the finished product with a high level of quality, but not unduly expensive to manufacture. In addition, they should provide characteristics comparable to those of conventional panels in terms of workability during on-site fabrication by the end user and architectural properties such as strength and stiffness.
Light transmitting panels comprising a light-weight honeycomb structure or other cellular structure, sandwiched between two light transmitting plastic sheets have been used in the past, but such prior panels have not possessed the combination of visual uniformity and structural performance of the present invention.
A major problem with prior light transmitting panels is the presence of fillets of glue (narrow areas of glue) which, because of past manufacturing techniques, tend to occur at places where the light transmitting sheet touches the edges of the cellular structure. The glue, not necessarily being perfectly transparent and having an index of refraction different from air, tends to prohibit, bend or deflect the flow of light. These fillets may be in the range of about 0.030 to 0.125 inches wide. Also using previous manufacturing techniques, the exact size and opacity of the fillet was difficult if not impossible to control due to the uneven migration of adhesive to the point of contact between the cell wall and face sheet. Liquid adhesives or adhesives that liquify during heating could tend in previous processes to run or drop to the lower face sheet due to gravity, resulting in larger fillets on one side of the panel. In addition, air trapped between an adhesive film and a translucent sheet can cause bubbles and other visual non-uniformities in a light transmitting panel. Previous methods of manufacture had a tendency to produce such defects, reducing the desirability and value of the panels in the architectural and design fields.
Another major problem occurring in current light transmitting panels, also due to manufacturing techniques that utilize adhesive films between the translucent sheet and the cellular structure, is the tendency of the film to separate from the sheet in areas between the edges of each cell. Because these separations alter the transmission and reflective properties of the panel, such panels have a visually non-uniform appearance.
While such non-uniformities may be acceptable for applications where panels do not transmit light, they are undesirable for panels in architectural and other design uses that transmit light and where visual consistency is important.
Methods of making honeycomb core panels have been known, but they have failed to provide the high degree of visual uniformity and other characteristics of the present invention. For example, Meier U.S. Pat. No. 5,667,867 relates to the use of two adhesive films, one applied to a sheet for an outer layer and one to a honeycomb core. The adhesive film on the core is treated to form droplets of adhesive at the edges of the cells of the core. The sheet and core are then brought into contact, and the droplets result in an adhesive contour, which is undesirable from the point of view of visual uniformity.
As another example, Fornier et al. U.S. Pat. No. 5,888,610 relates to using an adhesive film to bind a skin to a core, but the patent teaches heating the film to make the glue flow and bind the sheet to the core by forming a meniscus at the skin/core interface. Again, this flow and meniscus are undesirable in terms of visual uniformity of a light transmitting panel.
In another example, epoxy adhesive have been used to bind transparent sheets to cores. The epoxy has been applied to the sheet as a liquid and the core has been placed next to the sheet before the epoxy cures. In such cases, the liquid epoxy adhesive has flowed to areas of sheet/core contact, creating undesirable glue fillets.
As a final example, thermoplastic adhesive films have been merely placed between a translucent sheet and a honeycomb core, without first adhering the film to the sheet. This combination has then been heated above the flow temperature of the adhesive to bind the sheet to the core. The adhesive, however, has failed to adhere uniformly to the sheet, trapping air and causing bubbles and other visual non-uniformities. In addition, adhesive has migrated to areas of sheet/core contact, causing glue fillets and failing to provide the visual uniformity and other desirable characteristics of the present invention.
A preferred method of manufacturing light transmitting panels according to the present invention makes it possible to minimize or preferably eliminate glue fillets, bubbles or other trapped air, and film separations and to provide for substantial increases in the uniform transmission and reflection of light. Panels of this invention preferably may also provide other improved properties and interesting visual effects, including (a) directional translucency, wherein the structure of the cellular core produces different degrees of translucency depending upon the line of sight of the viewer through the panel, (b) translucency in proportion to the distance of the viewer from the panel, and (c) an effect that may be referred to as pixelation. Pixelation is the visual effect produced by capturing within each individual cell of the panel the color, intensity and movement of the light directly behind that cell. When viewed in conjunction with other contiguous cells within the context of a large panel, this property of the panel produces a visual effect simulating that of a digitized image composed of individual points of color and light, i.e., pixels.
This invention also makes it possible to obtain improved visual uniformity; to utilize economical raw materials; and to achieve a final product which is easily handled as a building or construction material.
The present invention includes a process for manufacturing a visually uniform, light transmitting architectural panel which comprises at least one light transmitting sheet, a film of adhesive, and a cellular structure. Typically, the cellular structure is a honeycomb panel which is sandwiched between two light transmitting sheets. That assembly is held together by two adhesive films, one on each side of the honeycomb panel. The adhesive film is adhered to the light transmitting sheet and the cellular structure, preferably without creating glue fillets or otherwise substantially altering the thickness of the film in large areas. This invention may be accomplished for example by using a heat sensitive adhesive film that has a flow temperature and heating the combination of sheet, film and cellular structure while in contact with each other to a temperature slightly below the flow temperature. Thereafter the temperature may be raised for a minimal time to above the flow temperature. As a result, the film does not alter its shape substantially, creates minimal or no glue fillets, results in little or no trapped air or bubbles, and does not have a significant tendency to separate from the sheet in areas that are not in contact with the edges of the cellular structure. Typically, the adhesive film initially has a uniform thickness which preferably it substantially retains throughout the manufacturing process.
In this manner a panel with a high degree of visual uniformity and/or a high degree of light transmission may be obtained. The panel may also possess novel or improved properties of pixelation, directional translucency and other desirable visual properties.